The present invention relates to a method of operating a wireless communication system and particularly, but not exclusively, to a method of adapting the wireless communication system to give good isolation from adjacent parallel signal streams.
A multiple input multiple output (MIMO) antenna system relies on transmitting a set of individual data streams on the same radio frequency from a set of xe2x80x9cmxe2x80x9d radio transmitters and receiving these data streams with a set of xe2x80x9cnxe2x80x9d radio receivers, each radio transmitter and receiver having its own antenna. The MIMO antenna system relies on having a propagation environment that is rich with scatterers such that each receive antenna obtains a substantially different set of signals from the transmitter. In order to assist further the process of separating the received signals nxe2x89xa7m. The technique can be used either to increase the robustness of a radio connection or to increase the capacity of the radio channel. Under ideal conditions a capacity increase of m may be possible.
Despite the simple requirements described, a MIMO antenna system requires complex signal processing. Two processes need to be performed, namely, the determination of the scattering matrix of the channel and the separation of the individual data streams. Furthermore, if the system is operating in not so ideal conditions some of the n receivers may not be contributing much to the detection process and hence represent a level of potentially expensive redundancy.
An object of the present invention is to operate a wireless communication system more effectively.
According to a first aspect of the present invention there is provided a method of selecting a combination of transmit antennas and receive antennas in a MIMO antenna system, comprising transmitting a first signal from a first of m transmit antennas, measuring a quality metric of the first signal as received at each of a plurality of n receive antennas, repeating the process using the remaining mxe2x88x921 transmit antennas to respectively transmit signals, and determining those combinations of transmit and receive antennas receiving acceptably a first signal and unacceptably a second signal and vice versa.
According to a second aspect of the present invention there is provided a method of operating a MIMO antenna system comprising a transmitter having at least two transmitters and a plurality of transmit antennas and and at least one receiving station having at least two receivers and a plurality of receive antennas, the method comprising transmitting a signal from a first of the plurality of the transmit antennas and determining a quality metric of the signal received by each of the plurality of the receive antennas, repeating the said operations using each of the remaining transmit antennas respectively, forming a channel matrix of the performances of the plurality of the transmit antennas versus the plurality of the receive antennas and selecting from the channel matrix a combination of at least two of the transmit antennas and at least two of the receive antennas in which a signal from at least one of the transmit antennas is acceptable at at least one of the receive antennas and unacceptable at the remainder of the receive antenna(s) and vice versa in respect of a signal from the remainder of the transmit antenna(s).
According to a third aspect of the present invention there is provided a MIMO antenna system comprising a transmitter station having at least two transmitters and a plurality of transmit antennas and and at least one receiving station having at least two receivers and a plurality of receive antennas, the transmitting station having means for sequentially selecting one of the transmit antennas and transmitting a signal from the selected transmit antenna, the receiving station having means for sequentially selecting one of the plurality of the receive antennas and means for determining a quality metric of a signal received by each of the plurality of the receive antennas, the system further comprising means for forming a channel matrix of the performances of the transmit antennas versus the receive antennas and for selecting from the channel matrix a combination of at least two of the transmit antennas and at least two of the receive antennas in which a signal from at least one of the selected transmit antennas is acceptable at at least one of the selected receive antennas and unacceptable at the remainder of the selected receive antenna(s) and vice versa in respect of a signal from the remainder of the selected transmit antenna(s).
By having more antennas than either receivers or transmitters gives the system plenty of freedom to select the best antenna combination such that the individual transmitter data streams can be received at those antennas that give the best isolation from adjacent parallel signal streams. Antenna redundancy can be practised with performance enhancements.
In implementing the method in accordance with the present invention the strength of the signals received by each of the receiver antennas from each of the transmitter antennas is measured using a simple antenna diversity selection process and a determination is made of the antennas which offer the strongest (or acceptable) reception as well as those that offer the weakest (or unacceptable) reception.